The purposes of this study are: 1) To determine the degree and specificity of antigenicity of nitrosourea induced brain tumors. 2) To determine whether or not nitrosourea-induced tumors can be used as a model for immunological studies of brain tumors. 3) To determine if and to what degree immune surveillance of tumor formation occurs in the CNS. 4) To search for an immunological mechanism of rejection of malignant nervous system tumors in experimental animals and 5) to search for immunological mechanisms that may help in diagnosis and therapy of human brain tumors. Central nervous system tumors (gliomas) induced in inbred rats with nitrosourea compounds will be cultured in vitro and will be transplanted intracerebrally and subcutaneously to isologous hosts, by solid tumor grafts and by tumor cell suspensions. Autochthonous and isologous hosts will be immunized against gliomas by repetitive subcutaneous exposure and removal of viable tumor grafts, by x-ray irradiated tumor grafts, and by antigen prepared from solid tumors plus Freund's adjuvant. The immunization will be tested by intracerebral tumor grafts. Lymphocytes, macrophages and serum will be obtained from tumor immunized animals, from animals with growing tumors, and from animals with operated tumors. The effectiveness of these cells and serum, upon brain tumors will be tested in lethally irradiated animals with implanted intracerebral gliomas, and in vitro by a cytotoxicity assay. The degree of antigenicity of nitrosourea induced gliomas, will be tested by intracerebral injection of a mixture of tumor-sensitized lymphocytes and tumor cells, in lethally irradiated animals.